Genetics is thought to be the cause in 80% of cases. The role of diet and cigarette smoking is unclear while neither cleanliness nor sunlight appear to be involved. Acne primarily affects skin with a greater number of oil glands, including the face, upper part of the chest, and back. During puberty, in both sexes, acne is often brought on by an increase in androgens such as testosterone. Excessive growth of the bacteria Propionibacterium acnes, which is normally present on the skin, is often involved.